Field of the Invention
The invention relates to drive gears which mesh together to form a gear pair and relates particularly to a gear pump or a motor which outputs an operating liquid using tooth grooves.
Description of Related Art
Conventionally, in a structure of a gear pump or a motor where gears which mesh together to form a pair are placed in a gear storing chamber, a gasket for preventing operating liquid from leaking to the outside is disposed between a body having the aforementioned gear storing chamber internally and a cover for covering the gear storing chamber of the aforementioned body. This type of gasket is placed in a gasket groove which is disposed on at least one of the aforementioned body and cover. The gasket groove has a shape which surrounds the aforementioned gear storing chamber, a low pressure port communicating with an inlet when being used as a gear pump, and a high pressure port communicating with an outlet when being used as a gear pump, and is non-symmetric to a line segment connecting the centers of the gears (for example, refer to patent document 1).
In addition, a material of the gasket used in this type of gear pump or motor is selected according to a composition and physical properties of the operating liquid. More specifically, in a typical hydraulic circuit, nitrile rubber is adopted in a case when the operating liquid is used at room temperature or near that temperature. Flurorubber is adopted in a case when used under high temperature conditions.
Here, as a method for discerning between gaskets that are made of different materials, color may be added to the gasket, or a shape of the gasket in a state where an external force is not applied may be made to be different.
However, when the method of coloring the gasket is adopted, dye needs to be mixed to the main raw material of the gasket, such as nitrile rubber or flurorubber, when the gasket is manufactured. As such, problems such as insufficient strength of the gasket may occur. In addition, an increase in cost is generated stemming from the additional processes during manufacturing and the increase in the types of raw materials.
On the other hand, when the shape of the gasket in a state where an external force is not applied is made to be different, the gasket which is formed from a first material (such as nitrile rubber) is made to a circular shape, and the gasket which is formed from a second material (such as flurorubber) is made to an asymmetrical shape to the gasket groove.
However, when the shape of the gasket in a state where an external force is not applied is made to be asymmetrical to the shape of the gasket groove, the following problems occur. Namely, after inserting a gasket having such shape into the gasket groove, the elastic deformation of the gasket in the gasket groove is very minute. As such, the gasket may fall out during the manufacturing process of this type of gear pump or motor when the surface where the gasket groove is disposed is faced downwards. In addition, since the gasket is an asymmetrical shape, the direction of the gasket must be matched when the gasket is attached.